The present invention detects malfunctions in a variable flow delivery pump. In the case of a metering pump, normal operation is necessary to maintain the accurate output volume. It is also important to detect malfunctions so that damages to the pump system are prevented. For example, the pumps described in Milton Roy, Instruction Manuals for maxRoy B (118.7) and HPD Milroyal B, C and D (60.3) have symptoms of malfunctions. The possible trouble-shooting procedures for these malfunctions are described. However, when malfunctions occur, an operator should be systematically notified of the malfunctions or the pump system should react to correct the malfunctions.
Performance can be monitored by pressure, torque, or flow rate. A number of patents address monitoring a piston pump to reduce substantially pulsation in its output. For example, U.S. Pat. No. 4,225,290 and U.S. Pat. No. 4,180,375 disclose a circuit to initiate an alarm for the pump shutdown in response to the abnormal pressure or motor over-torque fault conditions. The protection is provided by comparing sampled pressure, current, or torque values against corresponding preset absolute values. If a sampled value exceeds the predetermined value, the system may stop itself to prevent damage to the pump. However, with a variable speed motor, the detection of malfunctions using a predetermined absolute value is difficult because externally sampled values are dependent upon motor speeds or flow rates. In addition, since the prior art requires an expensive external monitoring device, there has been a need for an inexpensive monitoring system for variable flow delivery pumps.
The current invention is to detect conditions which cause disturbances to the inherently high accuracy (better than .+-.0.5%) in the metering pump. These conditions include wear, hydraulic, or external system malfunctions, or component damage. Without these conditions, the metering pump can maintain high accuracy in constant volume without adjusting operational parameters.
The current invention monitors the pump performance without comparing the sampled values to a predetermined absolute value. Force exerted on a displacement part in the pump and the displacement positions are measured in the current invention. According to a predetermined mathematical formula, the pattern of force and positional signals are analyzed to detect malfunctions.